The present embodiments relate to ultrasound transducers. In particular, switching usage of layers in the transducer is provided.
Bi-layer transducers provide a variety of operating modes not available in conventional transducers. By driving the two layers of an element in phase and then summing the received signals of the two layers out of phase, a harmonic mode is provided. The transmitted acoustic field has low second harmonic content, and received energy includes information at the second harmonic with fundamental frequency suppression.
U.S. Pat. No. 5,957,851 discloses a method for transmitting and receiving signals using layered acoustic elements. However, the method does not make use of both layers of the acoustic element for both transmitting and receiving. More optimum harmonic mode performance may be obtained when both layers of the transducer element are used.
The added flexibility of bi-layered elements comes at the expense of doubled channel count. Each element has two layers of transducer material, and each layer connects with different system channels. A transmit/receive channel is dedicated to each layer of each bilayer element. Transmitter waveforms and receiver signal processing can be optimized independently for each layer to realize the full potential of the bilayer transducer. The extra channel connections may be handled by the host system, but this requires a host system with two channels per element. An alternative is to build signal processing electronics into the transducer to direct transmit pulses to one or both layers of an element. The signal processing electronics phase and combine received signals from the layers. Active components in the transducer may require extra signal lines for control, may require extra power, and may generate undesired heat.
In the host ultrasound system, a transmit/receive (T/R) switch separates each channel into receive and transmit channels. The T/R switch is a passive switch, such as disclosed in U.S. Pat. No. 6,269,052. Active switching elements, such as a high-voltage CMOS analog switch, may not settle very rapidly. This makes it difficult to switch them during a scan line, such as between transmit and receive events for scanning a line. Operating active switching elements also requires carefully timed control signals from the ultrasound system.